WebSub to EventGrid via CloudEvents and Beyond

01-callback-1.cs

[FunctionName("CallbackAsync")]
public async Task<IActionResult> CallbackAsync(
    [HttpTrigger(AuthorizationLevel.Function, "GET", "POST", Route = "callback")] HttpRequest req,
    ILogger log)
{
    if (HttpMethods.IsGet(req.Method))
    {
        string challenge = req.Query["hub.challenge"];
        var result = new ObjectResult(challenge) { StatusCode = 200 };

        return result;
    }

02-websub-feed.xml

<feed xmlns:yt="http://www.youtube.com/xml/schemas/2015" xmlns="http://www.w3.org/2005/Atom">
  <link rel="hub" href="https://pubsubhubbub.appspot.com"/>
  <link rel="self" href="https://www.youtube.com/xml/feeds/videos.xml?channel_id=[channel_id]"/>
  <title>YouTube video feed</title>
  <updated>2021-01-27T07:00:00.123456789+00:00</updated>
  <entry>
    <id>yt:video:[video_id]</id>
    <yt:videoId>[video_id]</yt:videoId>
    <yt:channelId>[channel_id]</yt:channelId>
    <title>hello world</title>
    <link rel="alternate" href="http://www.youtube.com/watch?v=<video_id>"/>
    <author>
     <name>My Channel</name>
     <uri>http://www.youtube.com/channel/[channel_id]</uri>
    </author>
    <published>2021-01-27T07:00:00+00:00</published>
    <updated>2021-01-27T07:00:00.123456789+00:00</updated>
  </entry>
</feed>

03-callback-2.cs

    var payload = default(string);
    using (var reader = new StreamReader(req.Body))
    {
        payload = await reader.ReadToEndAsync().ConfigureAwait(false);
    }

04-websub-request-header.txt

Link: <https://pubsubhubbub.appspot.com>; rel=hub, <https://www.youtube.com/xml/feeds/videos.xml?channel_id=[channel_id]>; rel=self

05-callback-3.cs

    var headers = req.Headers.ToDictionary(p => p.Key, p => string.Join("|", p.Value));
    var links = headers["Link"]
                .Split(new[] { "," }, StringSplitOptions.RemoveEmptyEntries)
                .Select(p => p.Trim().Split(new[] { ";" }, StringSplitOptions.RemoveEmptyEntries))
                .ToDictionary(p => p.Last().Trim(), p => p.First().Trim().Replace("<", string.Empty).Replace(">", string.Empty));

    var source = links["rel=self"];

06-callback-4.cs

    var type = "com.youtube.video.published";
    var contentType = "application/cloudevents+json";

07-callback-5.cs

    var @event = new CloudEvent(source, type, payload, contentType);
    var events = new List<CloudEvent>() { @event };

    var topicEndpoint = new Uri("https://<eventgrid_name>.<location>-<random_number>.eventgrid.azure.net/api/events");
    var credential = new AzureKeyCredential("eventgrid_topic_access_key");
    var publisher = new EventGridPublisherClient(topicEndpoint, credential);

    var response = await publisher.SendEventsAsync(events).ConfigureAwait(false);

    return new StatusCodeResult(response.Status);
}

08-cloudevents-from-websub.json

{
  "id": "c2e9b2d1-802c-429d-b772-046230a9261e",
  "source": "https://www.youtube.com/xml/feeds/videos.xml?channel_id=<channel_id>",
  "data": "<websub_xml_data>",
  "type": "com.youtube.video.published",
  "time": "2021-01-27T07:00:00.123456Z",
  "specversion": "1.0",
  "datacontenttype": "application/cloudevents+json",
  "traceparent": "00-37d33dfa0d909047b8215349776d7268-809f0432fbdfd94b-00"
}

09-video-details.json

{
  "channelId": "<channel_id>",
  "videoId": "<video_id>",
  "title": "hello world",
  "description": "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis malesuada.",
  "link": "https://www.youtube.com/watch?v=<video_id>",
  "thumbnailLink": "https://i.ytimg.com/vi/<video_id>/maxresdefault.jpg",
  "datePublished": "2021-01-27T07:00:00+00:00",
  "dateUpdated": "2021-01-27T07:00:00+00:00"
}

10-video-details-to-cloudevents.json

{
  "id": "4cee6312-6584-462f-a8c0-c3d5d0cbfcb1",
  "specversion": "1.0",
  "source": "https://www.youtube.com/xml/feeds/videos.xml?channel_id=<channel_id>",
  "type": "com.youtube.video.converted",
  "time": "2021-01-16T05:21:23.9068402Z",
  "datacontenttype": "application/cloudevents+json",
  "data": {
    "channelId": "<channel_id>",
    "videoId": "<video_id>",
    "title": "hello world",
    "description": "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis malesuada.",
    "link": "https://www.youtube.com/watch?v=<video_id>",
    "thumbnailLink": "https://i.ytimg.com/vi/<video_id>/maxresdefault.jpg",
    "datePublished": "2021-01-27T07:00:00+00:00",
    "dateUpdated": "2021-01-27T07:00:00+00:00"
  }
}